Method of producing hollow blades



Sept. 19, 1961 l. E. HJELSTROM Filed April 5, 1958 INVENTOR. IRVING E. I'IJELSTROM n L\ V a y United States Patent ice 3,000,082 METHOD OF PRODUCING HOLLOW BLADES Irving E. Hjelstrom, West Caldwell, NJ., assignmto Curtis-Wright Corporation, a corporation of Delaware Filed Apr. 3, 1958, Ser. No. 726,099

' 7 Claims. (Cl.29156.8)

My invention relates to the production of hollow blades for compressors, turbines and the like.

The invention is concerned with producing a blade from a tubular member by forming such member to a desired blade contour in a press between suitable dies, while the member is pressurized internally by fluid or pneumatic pressure or both such that the member is caused to assume the die form upon the closing of the dies. The invention is particularly applicable to the forming of compressor stator blades, but is not necessarily limited thereto.

One of the difficulties involved in forming hollow blades while utilizing internal fluid pressure, is that pressure within the tubular material from which the blade is formed is instantaneously built up to a maximum at initial stages of the forming process, thereby prematurely the tubular member is limited by action of the press used in the forming process.

Other objects andadvantages of the invention will become apparent during a reading of the specification.

According to the invention a hollow tube of material from which the blade is to be formed is first closed at one end and filled from the other end with a fluid, such other end being connected to a substantially constant pressure source. The tube-is crimped to close off a length of the tubular materialfromthe pressure source and during the latter portion of-the crimping operation the blade contour is formed length of tubing such that pressure in the 3 tube is gradually increased during the forming of the blade to a maximum at a time when the crimping operation is complete. Excessive pressure within the tube is prevented by operation of the press itself.

The invention is explained in detail in the ensuing description which should be read in connection with the annexed drawing in which similar reference characters designate similar parts and in which:

FIGS. 1, 2, and 3 are diagrammatic showings illustrating successive steps in the method of forming a hollow blade according to the invention. Referring to the drawing reference character 1, designates a tube which is used in forming a hollow compressor stator blade according to the invention. The tube 1, is first closed at one end at 2, as by crimping. The other end of the tube is capped as at 3, and connected by conduit means 4, to a source of fluid 5, from which the tube is filled and subjected to the substantially constant pressure head. The tube may .be filled with water or any other suitable liquid. However, in the alternative a gas such as air, or both a liquid and a gas may be used in pressurizing the tube.

The tube 1, is situated in a press between U-shaped locators 6 and 7, which prevent lateral movement of the tube during the operation of the press. The press may be of the hydraulically operated type conventional in design. As shown, the tube rests upon crimpers 8 and 9, of the press above a fixed die 10. The crimpers 8 and 9, connect with fixed supports 11 and 12, through resilient means such as the springs 13 and 14. This 3,000,082 Patented Sept. 19, 1961 renders the crimpers 8 and 9, movable during the formation of the blade contour, and as will become clear hereinafter renders possible the relief of excessive pressure in the tube.

In carrying out the method of invention, the tube is engaged by a pair of movable crimpers 15 and 16, upon operation of the press, the crimpers 15 and 16 being located'directly above the aforesaid crimpers 8 and 9. The crimpers 15 and 16 press upon the tube such that the tube is squeezed and flattened as shown at 17 and 18 (FIG. 2) between the crimpers 8 and 15, and 9 and 16. As a' result of this squeezing and flattening the tube 1 is brought to bear against fixed die 10. The die 19 is caused to engage the tube after the crimpers 15 and 16, but before the wall of the tube is completely sealed at 17 and 18. Operations upon the tube are timed so that die action occurs during the latter portion of the crimping operation. The upper die 19 descends simultaneously with completion of the closing of crimpers 17 and 18, and there is a gradual build up of internal pressure within the tube between the crimpers due to the gradual restriction of the passage 20 through which fluid exits during the'closings of the crimpers and the die. Maximum pressure within the tube is attained when the die 19 reaches a final closed position which occurs substantially at the same. time as the sealing of the tube by the crimpers.

The build up of pressure within the tube length between the crimpers causes the tube wall between the dies to assume the die contour which defines a desired blade form in the final position of the die 19. The build up of pressure within the tube stretches the tube sections overhanging the dies to a point beyond the elastic limit of the material producing bulges 21 and 22 in the tube length between the dies and crimpers (FIG. 3). Pressure within the tube is relieved before opening the dies to avoid a distortion of the desired blade form by the internal pressure. Such pressure is readily relieved by piercing one or both of the bulged portions 21 and 22 of the tube. Thereafter the dies and crimpers are opened by the press, and the tube removed from the press and its connection to the fluid pressure source. Subsequent operations include trimming the processed piece to leave only a blade of desired form as defined by the dies and affixing it in the environment in which it is to be used, such as in a compressor stator as intended for the illustrated example. Since the crimpers 8 and 9 are resiliently supported, they serve as a form of relief valve in that if excessive pressure materializes in the tube, these crimpers open slightly against the springs 13 and 14 to permit fluid to escape through the crimped walls, in particular through passage 20. Obviously the springs may be selected to limit the internal pressure to any selected maximum.

It will now be apparent that the method described for producing a hollow blade is one having decided advantages. The method, which may be carried out on a conventional type of press, produces a product of uniformly high quality in that over-stressing is prevented by a gradual build up of internal pressure during the formation of the piece, also automatic relief of excessive pressures is regulated at the press itself eliminating the necessity of high pressure lines extending beyond the press with consequent danger to operators.

I claim:

=1. A method of forming a blade from tubular mate rial which method comprises closing an end portion of the tube, filling the tube with fluid and maintaining the fluid in the tube under pressure from a connected pressure source, crimping the tube to close off a length of tube from the pressure source, and forming the blade contour in said length of tube during the latter portion of the crimping operation whereby pressure in the tube is gradually increased during the forming of the blade to a maximum at the time when said crimping operation is complete.

2. The method of forming a blade as definedin claim 1 wherein the crimped portion of the blade is resiliently restrained against fluid pressure during formation of 'the a blade contour such that excessive fluid pressure in the tube length may be relieved through said crimped portion.

3. A method of forming a blade from tubular material which method comprises closing an end portion of the tube, filling the tube with fluid and maintaining the fluid in the tube under pressure from a connected pressure source, crimping the tube to close off a length of tube from the pressure source, forming the blade contour in said length of tube between dies during the latter portion of the crimping operation whereby pressure in the *tube is gradually increased during the forming of theblade to a maximum at the time when said crimping operation is complete, and relieving fluid pressure in the said length of tube before opening the forming dies.

4. A method of "forming a blade from tubular material which method comprises closing an end portion of the tube, filling the tube with fluid and maintaining the fluid in the tube under pressure from a connected pressure source, crimping the tube to close ofi a length of tube from the pressure source, forming the blade contour in said length of tube between dies during the latter portion of the crimping operation whereby pressure in the tube is gradually increased during the forming of the blade to a maximum at the time when said-crimping operation is complete, said blade contour'being formed over only a portion of the said length of tube whereby other portions are bulged during the forming operation by fluid pressure inthe tube, .and piercing the bulged portions of the tube to relieve pressure .therein before opening said dies.

5. A method of forming ablade from tubular material whichmethod comprises closing one end portion of the tube, filling the tube with fluid and maintaining the fluid in the tube under pressure from a pressure source connected to the other end of the tube, crimping the tube at select stations defining a length of tube therebetween, forming the blade contour in said length between dies during the latter portion of the crimping operation whereby pressure in the tube is gradually increased during the forming of-the bladeto a maximum at the time when said crimping operation is complete, said blade contour being formed over only .a portion of said length of 'tube whereby the portions of said length between the crimping stations and dies are bulged during the 'forming operation by fluid pressure in the tube.

6. A method of forming a blade from tubular material which method comprises closing an end portion of the tube, filling the tube with fluid and maintaining the fluid in the tube under pressure from a connected pressure source, crimping the tube to close ofi a length of tube from the pressure-source, forming the blade contour in said length of tube between dies during the latter portion of the crimping operation whereby pressure in the tube is gradually increased during the forming of the blade to a maximum at the time'w'hen said crimping operation is complete, and relieving fluid pressure in the said length of tube, opening said dies and removing the tube, and trimming excess material from the tube to leave a desired blade form defined by the'dies.

7. A method of forming a blade from tubular material which method comprises closing an end portion of the tube, filling the tube with fluid and maintaining the fluid in the tube under pressure from a connected pressure source, crimping the tube to close off a length of tube from the pressure source, forming the blade contour in said length of tube during the latter portion of the crimping operation whereby pressure in the tube is gradually increased during the forming of the blade to a maximum at the time when said crimping operation is complete, and relieving excessive pressure in the tube by opening the .crimped portion of the tube.

References Cited in the file of this patent Staples Oct. 28, 1958 

